Where is sculpt vertex paint in 2.92?
Get an alpha version and Enable Develope Extras
Since somwhere around 2.9 version series appeared, some experimental features are hidden by default (they are not ready yet, we don't want a basic user to mess their file with them).
You can enable experimental fetures by enabling the Developer Extras checkbox in the Preferences.

Then the Experimental tab appears and you can choose the feature to enable.
Vertex color in sculpting is the first one.

You could probably find the features while 2.92 was in aplha or beta version, but nowadays that the version has become official, it was removed.
You are more likely to find them in old 2.92 alpha versions, current alpha versions, custom builds...